This application claims the priority of German patent document 100 19 770.1, filed Apr. 20, 2001, the disclosure of which is expressly incorporated by reference herein.
The invention relates to an improved method and apparatus for improving cold-starting of catalytically active components in gas generation systems of mobile fuel cell systems.
It is known that catalytically active components (for example a CO oxidation stage) in gas generation systems are difficult to start at temperatures below the operating temperature, on account of the catalytically active centers being filled. Filling with CO or condensing constituents such as water or fuel (e.g., methanol) has caused particular problems, since it may impede the mass transfer (and therefore the catalytic activity) in the catalytically active component. In the case of water, at low temperatures icing of the catalyst may occur.
To heat catalytically active components rapidly to operating temperature, it is known to burn fuel either inside or outside the particular component which is to be heated. Another possible option is to burn fuel in a further component which is in thermal contact with the component to be heated.
It is an object of the invention to provide a method for quick and reliable cold-starting of catalytically active components in gas generation systems.
This and other objects and advantages are achieved by the method according to the invention, in which a temporary store is arranged directly in the starting-material gas stream. This storage unit stores gaseous constituents from the starting material of the component that is to be started, which constituents cause difficulties when starting, and therefore protects this component from bing filled by these constituents. It is possible in particular to store CO and condensing constituents such as water or fuel (in particular methanol).
As a result of the ongoing heating of the system as operation continues, in particular after the operating temperature (which is typically 200xc2x0 C.-300xc2x0 C.) has been reached, the temporary store releases the stored components again, and thus regenerates itself for the next cold start.
The temporary store therefore performs a type of buffer function, is thus also referred to in the text which follows as a buffer.
The temporary store according to the invention can be used in particular to protect the following components within a gas generation system:
a catalytic burner for controlling the temperature of the system;
a reformer for fuel gas generation for the fuel cell;
a reactor for the partial oxidation for fuel gas generation; and
a CO oxidation stage or a membrane for cleaning the fuel gas.
The method according to the invention is particularly suitable for protecting components in which an exothermic reaction takes place.
The buffer according to the invention can be designed as a combination of a plurality of storage components, the individual components being selectively suitable or optimized for storing a specific substance.
Furthermore, the temporary store may comprise components which operate on the basis of different chemical-physical storage principles.
In a preferred embodiment, the temporary store is designed as an adsorber.
In an advantageous embodiment, the temporary store is an adsorber with a large surface area and Cu-containing support material, for example a zeolite. Other suitable materials are Al2O3 or activated carbon. Such materials are particularly well suited to the adsorption of CO, but may also be used for the adsorption of methanol or water.
The method according to the invention is particularly beneficial if, in a component which is to be protected from CO, the catalytic material of this component is on a metallic or ceramic support structure (monoliths, metal sheets), since the high heat absorption capacity of these structures makes it very difficult for the catalyst to be ignited in CO-containing gas.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.